The invention relates to a power supply circuit for a discharge lamp, comprising an electric power source outputting a d.c. voltage and capable of reabsorbing electrical energy, which also comprises an energy transferring circuit inserted between the electric power source and a first capacitor connected to the lamp, the capacitor being charged via the energy transferring circuit and adapted to store the energy required for each discharge across the lamp.
More particularly, the invention relates to a power supply circuit for a flash lamp used as a light source in an optical analysis device such as, for example, a rotary spectrophotometer, i.e. a spectrophotometer in which samples carried by a rotor pass in rapid succession in front of the optical head of the spectrophotometer.
It is known to use supply circuits for discharge lamps used in stroboscopes. A circuit of this kind is described in the publication: "Instruction Manual, Strobotac type 1538-A, General Radio Co.". At each discharge, the last-mentioned circuit supplies a fixed voltage value between the anode and the cathode of the discharge lamp, for producing flashes at an adjustable frequency from 2 Hz to 2500 Hz, in four ranges. The known supply circuit has a number of disadvantages, if intended for use in an optical analysis device:
1. The design of the circuit is such that if the frequency range is high, there is a corresponding reduction in the capacitance of the capacitor supplying energy for each discharge (i.e. the capacitance varies from 1.1 .mu.F to 0.007 .mu.F). As a result, the energy available per discharge (E=CV.sup.2 /.sub.2) decreases when the frequency of the discharges increases. Consequently, the charging power (P=E/.DELTA.t where .DELTA.t=1/.DELTA.f) remains below 6 W all the frequency ranges, which is quite insufficient for the requirements of rotary spectrophotometers.
2. Since the voltage supplied by the known circuit to the lamp is fixed for each discharge, one cannot modify the light amplitude of the resulting flashes; such modification is desirable, e.g. when the discharge lamp is used as a light source in a spectrophotometer, i.e. when it is necessary to vary the intensity of the light flashes in order to compensate differences in light output at the various wavelengths under consideration, preferably under the control of an automatic programmed system.
3. When it is desired to operate with the maximum energy available for discharging, the frequency of flashes is limited by the time taken to recharge the capacitor supplying energy for each discharge. For example, when the energy available for discharging is at a maximum (E=1.1 .mu.F (800 V).sup.2), the recharging time required is about 80 msec, which corresponds to a relatively low flash frequency and is insufficient for certain applications, e.g. in rotary optical analyzers.